1. Field of the Invention
The present invention relates to a thermal image analysis system for analyzing the temperature on the surface of a subject by taking an infrared image of the surface of the subject through a combination of an optical system and an image sensor and processing the information of the taken image. The present invention particularly concerns such a thermal image analysis system having a function of performing the thermal image analysis with respect to the information of an image reproduced after the image information outputted from the thermal image analysis system has been recorded in an image recording/reproducing apparatus.
2. Description of the Prior Art
FIG. 13 exemplifies a thermal image analysis system constructed in accordance with the prior art, as disclosed in Japanese Patent Laid-Open No. Sho 58-120136. In FIG. 13, reference numeral 1 denotes a thermal image analysis system; and 2 an image recording/reproducing system. The thermal image analysis system 1 comprises a sync separation circuit 3, a delay circuit 4, a sample-and-hold circuit 5, a level judgment circuit 6, a thermal image analyzing unit 7, an image input circuit 8 and an image output circuit 9.
The analysis of the thermal image analysis system 1 will be described below.
FIG. 14(a) shows a waveform of an image output signal from the thermal image analysis system 1 to the image recording/reproducing system 2. Sync signal parts are designated by symbol p while absolute temperature signal parts inserted to measure absolute temperatures are indicated by symbol r. The signal level R at each of the signal parts r is variable depending on the range of temperature in the thermal image analysis system 1 and will be recorded in the image recording/reproducing system 2 with the information of thermal image when an image signal is outputted from the image output circuit 9 and recorded in the image recording/reproducing system 2.
As the image signal is reproduced by the image recording/reproducing system 2, the signal level R is also reproduced with the thermal image information in the same form as shown in FIG. 14(a). In the thermal image analysis system 1, the sync separation circuit 3 only fetches such sync signal parts as shown in FIG. 14(b) from the image signal shown in FIG. 14(a). The delay circuit 4 retards the fetched sync signal parts by a given time t.sub.d to form such a signal as shown in FIG. 14(c).
The delay circuit 4 is set so that the delayed sync signal parts are located at positions corresponding to the respective absolute temperature signal parts r. The sample-and-hold circuit 5 samples and holds the image signal shown in FIG. 14(a) at the sync signal parts shown in FIG. 14(c) to provide an invariable signal having its level equal to the signal level R in the absolute temperature signal parts r, as shown in FIG. 14(d). As a result, the level judgment circuit 6 can easily know the range of measured temperature in the thermal image analysis system 1 when the image signal is recorded in the image recording/reproducing system 2.
The thermal image analysis system 1 is manually or automatically set on the thus judged range of measured temperature such that the thermal image analysis can be carried out under the same condition as that of the recording step.
In such an arrangement, however, DC components will be superimposed on the image signal or the dynamic range will be undesirably changed when the reproduction is carried out after the recording in the image recording/reproducing system 2. In other words, the signal level R may be changed so that a correct judgment will not be made from only a single signal level. This tends to cause incorrect judgment. Thus, the thermal image analysis system 1 of the prior art shown in FIG. 13 can at most recognize several steps in the range of measurement through judgment from the signal level R. It is impossible for the range of measured temperature to be finely regulated and set in the image recording/reproducing system 2 before re-measurement.
It is therefore an object of the present invention to provide a thermal image analysis system which can compensate for any degradation or variations in an image signal due to the image recording/reproducing system and improve the accuracy of the thermal image analysis.